This paper examined the effect of the increasing flexibility of labor market on the National Pension System. We have utilized the actual records of the Nation Pension Corporation to compare the status of salary workers in between years of 1998, 2000, and 2003. The main focus of the paper is on the salary workers who leaves job in the year of 1998 and 2000 and their participating status of the National Pension System in 2003. We found that job quitters in either 1998 or 2000 who are found to be employed in 2003 have reported higher earnings than those who are found to be self-employed in 2003. We also found that average tenure of the employed workers are getting shorter in recent years. The most of workers who left jobs in 1998 or 2000 could not move to another employed position and became self-employed or out of labor market. This trend will threaten old-age income security of those who have been laid off in early 40's and older after retirement. This paper recommends measure that could deter trend of private labor market culture of shying away from long-tenured workers